23' car roof jon boat

First attempt was to build a nest boat cut in half. But I don't know if it's too much hassle during assembly.
I'm leaning towards a one-piece build.
Crew 2+2, crew weight 230kg.
LOA 23' (7m)
BOA 49"-52" (125-130cm)
Freeboard: 27"(60cm)
Draft: nothing
Hull weight for roof transport : (???)
Propulsion: 2x 30 hp 2stroke prop.
Propulsion options: 1x50hp 2stroke, 2x50hp 2 stroke, 1x70-90hp 2 stroke, 1x60hp 4 stroke, prop or jet.
Weight of the engine/s around 100-150 kg.
Single engine setup make cumbersome engine hookup shorthanded.

 

Of course I know that there are boat trailers, but my tradition is a boat on the roof. It will probably end with a trailer. Someday.
A trailer means speed limits, difficult offroad handling.SOR is little bit challenging but I like it.

 

Purpose of the boat :
https://hydro.imgw.pl/#/
skinny water 100km+ distance , fuel efficient .

 

Hi montero. Draft zero = you are dreaming. 230Kg + 1 or 2 outboards + your extra gear and fuel will get you several inches of draft at least. 2 outboards on 130 cm beam will be a busy stern. Fuel for 2 x 2 strokes for 100 Km will not be light, even if going slow; 2 strokes are not fuel efficient by nature. How do you intend to lift it to your roof? Do you own a Hummer, or something stable enough to take a long 'heavy' roof load? You will be speed restricted anyway, especially taking corners, and in high head and cross winds. Mounting the OB's at the water will be about the same work as assembling a nested hull.
Buy a junk boat on a good trailer, and sell the boat, then adapt the trailer to suit.

 

Why do you anticipate all that horsepower for a rooftop boat? Is all out speed one of your priorities or do the other requirements take precedence. Sure enough it is possible, perhaps even practical under certain circumstances, to cartop a 23 foot boat. That had better be a lightweight boat not more than 100 kg and preferably less. Even if 100kg or less, you will need some strong help to load and unload such a boat. Then you will need more strong help to lift and install a hundred kg engine.

 

Are there cars with strong enough roofs to carry such a boat?Doesn't seem likely to me,and then there might be limitations on the permitted overhangs.Buy a truck with an articulating arm for lifting or buy a trailer,it would make it possible but not exactly convenient.The concept seems to be too close to the desire for a seaworthy ocean crossing sailboat that will sleep five and can be cartopped and people occasionally ask about such things.

 

Even small vans have a roof load capacity of 150 kg.

Emergency sleeping for 4 , without pitching a tent is one of the assumptions.
That's why boat is that long.It's long also to keep noise away from childs.
Flipping windshield upper edge , hook asian style bimini .Open sides , optionally covered by rolled mosquito nets / raincovers .
2 meters long stern area will be open .

 

Bolger "folding schooner" or a Michalak Blue Laguna. Get a 4 to 6hp 4-stroke. Even rivers have speed limits.

 

Zero draft I mean at speed.
I once dug into a sandbar to moor and water came through the transom .Thats normal for over powered jon boat . OB weight was 62kg , BOA 90cm LOA 5.5 m.
Lot of fuel and , -15degC by the way.Alot of gear for winter camp.
Top boat loaders .

 

That would require a levitation system.

 

Then you need a hovercraft. Anything else has a prop in the water and even jets have induction scoops, so not, zero draft.

 

Hull from free version of Delftship(online database, recreational, BrierCrek stretched to close to SOR dims)
60HP Motor and people off Grabcad
Also wondering about 'cartopping''such a large boat.

 

The FAO boat plans could be used as a base for your design and be redesigned to take an outboard . The 4 designs run from a 17' loa with 6' beam to 28' loa with a 6' beam , if you scale to 23' and assume the 6' beam of the 28' can be scaled down to fit the 23 then you will be close to your target beam . Building lighter would also have to be factored in .

 

I've seen a folding schooner folded and unfolded a few times at Texas 200 events. IMO it's a scary deal both ways, a lot of weight to come crashing down folding and unfolding. I've designed marathon racing canoes up to 50' +/- that were carried roof top but needed extra supports at each end of vehicle, pickup trucks were usually used. Some special permit requirements kicked in at the 40' mark.
Regarding your current design, how fast do you want to go? In this part of the world the standard power for flat bottom skiffs running in real shallow water (duck punts) is a mud motor. A mud motor would seem to be well suited to your needs.